The genes encoding the antigen-binding proteins of the immune system are assembled from arrays of DNA segments during lymphoid differentiation. The VDJ recombination activity (recombinase) is the essential lymphoid enzyme system that catalyzes this assembly process in early B and T cells. Insofar as the generation of the antigen-binding proteins is the primary function of lymphoid cells, this enzyme plays a central and critical role in the immune system. Yet there is currently no cellular assay for this activity in human cells. This represents not only a significant deficit in human immunology, but also a critical absence in human pathology. The VDJ recombinase mistakenly catalyzes the chromosomal translocation events in several malignancies. These include most endemic Burkitt and follicular lymphomas, and some pre-B acute lymphoblastic leukemias, diffuse B-cell lymphomas, myelomas and chronic lymphocytic leukemias. In this project, I plan to develop an assay for the VDJ recombination activity in normal and neoplastic human cells. The assays would parallel one that I recently developed for murine cells. The first steps are to identify a viral vector that will drive replication of the VDJ recombination substrate upon entry into the lymphoid cells, and subsequently to efficiently recover and measure the extent of VDJ recombination of the plasmids. This will then allow a survey of 60 to 80 human cell lines from hematopoietic malignancies for levels of VDJ recombination activity. Concurrently, measurements on primary human T cells from thymus will be done. The fidelity of the recombination process will be examined to assess if a predisposition to chromosomal translocations exists in hematopoietic neoplastic cells. These measurements and assessments of VDJ recombination activity and fidelity will be correlated with the developmental stage of the primary and neoplastic cells, surface marker phenotype, status of endogenous immunoglobulin or T-cell receptor rearrangements, histology, cytology, and cytochemistry of the neoplasms, and presence of chromosomal translocations. In this way, we will establish a developmental profile of this key enzyme of the immune system. This will allow comparisons between normal and neoplastic cells, and allow inferences regarding molecular etiology and pathogenesis in a major fraction of hematopoietic neoplasms.